Dragon Rocketry 4" Exocet MM38 Unboxing & (Eventual) Build

[KenECoyote]

Getting gluey!

I have a variety of glues and epoxies and I chose simple hobby 5/6 minute epoxy since I had it handy and it's quick and easy. If I was planning to pushing the rocket to extremes, I'd choose better stuff, etc., but after finding out how strong this 5 minute stuff is to break in my Phoenix Build, I think it's plenty enough here. Ymmv

Edit: It is a good idea to sand off the glassine where you'll be gluing so the epoxy sticks better. Also A good tip is to wrap a sheet of paper around the tube and use a marker to draw completely around the tube where the CR goes.

The forward CR is close to/abuts the forward fin root, so you don't want a thick fillet on there otherwise it may interfere with the fin sitting flush on the motor tube unless you grind off some epoxy or take a bit off the root corner.

The middle CR was a bit loose, so as the epoxy hardened, I kept checking that it wasn't crooked.

After the epoxy hardened, I used a dremel sanding drum to chamfer the forward edge of the middle CR to make it easier to insert and so it wouldn't mess up the rear lip of the bt.



I also brushed CA onto the bt aft end to strengthen it (I turned on my overhead filtering fan for this due to the fumes).

 

[KenECoyote]

I also test fit the assembly into the bt and it was nice!


I then spotted something...




To be continued...

 

[DRAGON64]

Many moons ago, a HARA member flew his Exocet, a kit made by Black Hawk R&D (long since defunct mfg), using HyperTEL L hybrid motors.

 

[KenECoyote]

I then spotted something...
View attachment 549537



To be continued...

So how is it KenECoyote doesn't know his aft from his elbow?

When there are two "afts" of course!



It turns out that the motor tube was marked "aft" on both ends and I hadn't noticed - they were on opposite sides of the motor tube, which is likely why the person marking also missed this. No biggie since the markings are about symmetrical; however, it did lead to a few points of slight confusion.

 

[KenECoyote]

This is a great reminder to check, check, check. You can't always account for every error, but extra effort checking before gluing will save you a bunch of headaches.

I used to work a job that demanded no errors since the data I was providing would be used the next morning to decide on multimillion dollar national ad campaigns and I went three years without any major error. The biggest lesson I learned is that everyone makes errors and once you remember that, it helps to keep you on your toes.

Another thing is that it's been a while since I've done a HP build and it seems I've forgotten some things (which I conveniently remember after lol) and this being a rocket with mid fins complicates thing a lot, but it's an adventure doing a build thread and figuring things out along the way!

 

[KenECoyote]

Back at it.

So now I focused my attention on the aft. I already checked that it was good before gluing the CRs, but now to mark it off and fine tune. (Note: it may be better to have done this as a first step).

I added on the motor retainer to confirm where it ends since the aft CR goes back there too. (BTW - Let me know if the pics are too big...I'm posting from my phone, so I can't tell.)

 

[KenECoyote]

Moving forward...

Ideally, the motor tube should go as forward as possible to bring the CG forward a bit; however, there's limited space back there and the aft CR goes up against the rear fins.

Once satisfied with the rear markings, I continued planning on the assembly insertion into the body tube.

One important thing to check is that you DON'T have the assembly glued in where the eyebolt nut is blocking a fin slot...bad, bad.

So I planned to have it arranged so that the eyebolt is opposite the rail buttons (which are centered between the fins already). Thus also avoids that bit of extra weight on one side in my opinion. It's easier to notice a rocket veer a bit to the side vs forward or backward (one of my secrets to straight flights).



Once happy, I used a screwdriver to score where the mid fins go and then marker it up.

 

[KenECoyote]

Check!


Now I was getting closer to gluing and added more markings. One is to check for alignment on every mid fin slot just in case and the others were dotted lines where the CRs go so I know where to apply the epoxy inside the bt and can then mark off a stick for such.



That's it for now, thanks for following!

 

[Handeman]

Looking good.

Just a super minor thing you might want to consider on your next build. If you turn the eye-bolt slightly, making sure it doesn't interfere with the MMT or BT, it will give you more clearance, making it just a little easier to thread your shock cord through. It might allow you to us a quick link where it might not otherwise fit.

 

[KenECoyote]

Looking good.

Just a super minor thing you might want to consider on your next build. If you turn the eye-bolt slightly, making sure it doesn't interfere with the MMT or BT, it will give you more clearance, making it just a little easier to thread your shock cord through. It might allow you to us a quick link where it might not otherwise fit.

Great note, thanks! I checked with a meaty quick link and it goes in fine. Still, it's better to angle it for easier access.

 

[DragonRocketry]

I guess I need to write AFT bigger on the parts next time...LOL. Looking good.

 

[KenECoyote]

I guess I need to write AFT bigger on the parts next time...LOL. Looking good.

Thanks!
It was written small, but the bigger issue ended up being that both ends were marked "aft". Apparently it was accidentally marked on both sides differently. Just clarifying so you're aware of it, but it wasn't any issue beyond some initial confusion on my part.

 

[KenECoyote]

Back and forward.

I had pondered about how to best glue in the mmt assembly. In the end, I decided to first apply an epoxy ring inside the bt for the middle CR from the aft end and then insert the assembly from the front.

This was because the mid CR glue area would be easier to reach than the front CR. Also if I inserted from the rear, the front CR would take almost all the mid CR epoxy ring I applied and just smear it through the bt as well as through the mid fin slots. Then trying to apply more epoxy to the mid CR would be difficult with the motor tube in the way. Tough thinking through the mid fin situation!

Before the epoxy was set, I made sure to check fin slot alignment (somehow I remembered!)...


Also before the epoxy was set, I added a rear fin atop check the clearance and alignment aft.



Then after it was set, I applied an epoxy fillet to the front CR by mixing it in a small cup (little plastic ketchup cups I think I got at Wendy's), then reaching in from the front and pouring it on the front CR while slooowly rotating the bt so it would drip around in a ring. A bit messy, but worked pretty well.

 

[KenECoyote]

Fin fickle.

So now I'm ready to epoxy the fins on. Thinking through, it makes more sense to glue the rear fins first and then use them to align up and glue the mid fins using angle stock and clamps.

On my last build (4" Madcow Patriot), I used a cardboard fin jig, but it wasn't ideal and I wasn't happy with the results.

Years ago I searched for a fin jig, but it seems that it's either cheap or $500 lol. Still seems to be the case except for 3D printed jigs.

I spent a few hours last night looking for a 3D print file for 4" 4 fin rocket and I didn't find much and my printer doesn't seem big enough.

So I'm brainstorming my own fin jig. I don't think I've seen similar before. I'll see if I can make it this weekend and test it and I'll report back.

 

[DragonRocketry]

If anyone is interested in one of these, I have enough parts for one more kit. Message me if interested as it is first come.

 

[KenECoyote]

If anyone is interested in one of these, I have enough parts for one more kit. Message me if interested as it is first come.

If anyone is interested, better jump on this. I'm not affiliated, but I love this kit!

BTW - Dragon Rocketry also has free shipping this weekend...

Last of the holiday discounts, Free shipping weekend. Orders of a $100 or more will ship for free, just use code FREESHIP at checkout and your shipping is on me. This will end at midnight 12/11, so do not miss out.

Dragon Rocketry Store

Thank you all that have support me. This has been an awesome year and looking forward to adding more things for next year.

 

[jmasterj]

I have one of these as well, haven't done much with it. Installed the motor mount and got hung up on beveling the forward fins before installing them.

I did print a new nose cone, though. I didn't really like the attachment options given that I needed to add nose weight. My print is cleaner, too.

 

[jmasterj]

Fin fickle.

So now I'm ready to epoxy the fins on. Thinking through, it makes more sense to glue the rear fins first and then use them to align up and glue the mid fins using angle stock and clamps.

On my last build (4" Madcow Patriot), I used a cardboard fin jig, but it wasn't ideal and I wasn't happy with the results.
View attachment 550018
Years ago I searched for a fin jig, but it seems that it's either cheap or $500 lol. Still seems to be the case except for 3D printed jigs.

I spent a few hours last night looking for a 3D print file for 4" 4 fin rocket and I didn't find much and my printer doesn't seem big enough.

So I'm brainstorming my own fin jig. I don't think I've seen similar before. I'll see if I can make it this weekend and test it and I'll report back.
View attachment 550019

@DragonRocketry sells fin jigs now!

 

[DragonRocketry]

I have one of these as well, haven't done much with it. Installed the motor mount and got hung up on beveling the forward fins before installing them.

I did print a new nose cone, though. I didn't really like the attachment options given that I needed to add nose weight. My print is cleaner, too.

Send me picture of your nose cone please.

 

[KenECoyote]

@DragonRocketry sells fin jigs now!

Oh dang it! LOL. I think I saw the fin jigs at one point and figured I'd pick it up later, but completely forgot. Very nice!

 

[KenECoyote]

Getting jiggy with it!

More work on my custom fin jig. Getting there...still need two more features (center adjustable standoff & support and a thin metal rod in the back to gauge the fin's vertical alignment (and maybe some small add-ons to improve).

 

[Back_at_it]

Nice build. I have picked up a few kits from Dragon this year and I'm really happy with the quality of the materials and how complete the kits come.

I too have found some minor inconsistency with marking and fin slots but etc. but nothing that is going to stop me from buying their kits. They sell a great product at a great price and it's marketed to experienced builders.

 

[DragonRocketry]

Nice build. I have picked up a few kits from Dragon this year and I'm really happy with the quality of the materials and how complete the kits come.

I too have found some minor inconsistency with marking and fin slots but etc. but nothing that is going to stop me from buying their kits. They sell a great product at a great price and it's marketed to experienced builders.

Please let me know what inconsistencies you found, so I can improve the quality of the product.

 

[KenECoyote]

Fin jig is almost done. I got the two parts in and just need to make sure the rod is aligned correctly.



The jig I made is modular so I can use it with other parts for other rockets with maybe some new parts or adapters.

 

[KenECoyote]

Here's pics showing the rod used for vertical alignment.

Good:


Bad:

So I just need to make some final adjustments and expect to then try this jig out on the Exocet. Hope to have all fins tacked in place by this weekend.

 

[dpower]

Great looking kit, I really like more complex scale HPR kits like this.

 

[KenECoyote]

I've been busy...life of a brainstorming multitasking mad scientist rocket builder! I've been seriously sidetracked building not one...but three unique design Christmas rockets! These are kinda time sensitive.

 

[KenECoyote]

I've done a bit of fine tuning and fitting on my jig (still a bit more needed, but it's good enough for now).

I've started by first adding some 5 minute epoxy to the rear motor tube where the rear fin will seat. I did this using a popsicle stick from the rear - I just need to tack it well in place since:

• Later I'll be adding internal epoxy fillets
• Trying to goop on epoxy to the fin and inserting can be messy
• I don't want too much epoxy back there yet because I still need to add back the rear CR.
• Not gluing the fin to the outer body tube yet also helps with final alignment since there is still a bit if play to insert the rear CR. I've had at least one case where it wouldn't get in place after the TTW fins were also glued to the outer bt.

I also checked where the rail buttons would go so that the cool dragon logo fin would face out.


After the rear fin was set, I added epoxy into the mid fin slot, then buttered up the fin itself with epoxy and inserted. Then added my jig with an extra clamp just in case.


I added a piece of tape to the forward fin edge since it's so long and can easily slip a bit before the epoxy cures. I gotta say...the predrawn lines are awesome on this kit!

 

[KenECoyote]

I think it looks great...very happy with my jig so far.

I'll try to tack the rest in place tomorrow night.

 

[cautery]

I think it looks great...very happy with my jig so far.

I'll try to tack the rest in place tomorrow night.

I do believe that constitutes "proof of concept"! Congratulations!